How to Have Twins With the Dairy Diet

How to Have Twins - Drinking Milk
How to Have Twins - Do milk and dairy products cause twins?. View Stock / Getty Images

There are so many theories about the causes of twins. Some theories are grounded in scientific fact, and some are anecdotal. Every family probably has their own theory, but one that has been bandied around in recent years is a connection between a diet high in milk and dairy products and an increase in twins. 

In 2006, a study was released suggesting that women who include dairy products in their daily diet are five times as likely to have twins than their vegan sisters. The May 2006 issue of The Journal of Reproductive Medicine included a report from a doctor at the Long Island Jewish Medical Center that concluded that the consumption of dairy products raises a woman's chances of conceiving twins. The study was widely reported in popular news sources such as The New York Times, BBC News, and LiveScience, and the coverage led many people to believe that a direct rich in dairy can increase the chances of having twins. 

Here are some details about the study. Dr. Gary Steinman of the Long Island Jewish (LIJ) Medical Center in New Hyde Park, NY studied three groups of women:

  • Vegans (those who ate no animal products at all)
  • Vegetarians (those who didn't eat meat but did consume dairy products)
  • Omnivores (those who ate meat, including dairy products)

The results of his study showed that the group of vegan women had twins much less often — in fact, five times less — than the other groups.

His theory was that Insulin-like Growth Factor (IGF), a protein that helps embryos survive during the early stages of development, is elevated when cattle are given growth hormone to increase their production of milk and beef. When women ingest the milk from these animals, their own hormones react, stimulating ovulation.

He connected his theory to the rapid rise in multiple births in the last thirty years. The increase had often been attributed to advanced maternal age and increased use of fertility technology. However, this study suggested that dietary habits might also be a factor.

It would also explain why an increase is only evident in fraternal, or dizygotic twinning, which results from the fertilization of multiple eggs. Identical, or monozygotic, twinning rates have remained unchanged. Monozygotic twins occur when a single fertilized egg splits into two. As of yet, no one has clearly identified the causes of monozygotic twinning.

New Evidence About Twinning and Dairy

In the years since Steinman's original study was released, the theory has been called into question. A subsequent review found flaws in the study, including a biased study sample. Contradictory evidence shows that the that IGF levels in treated cows are minimal and that the impact of digesting it through consumption of milk products is negligible in humans. So, the connection between a dairy-rich diet and increased twinning remains dubious. It is more likely that poorer overall nutrition among vegan women who participated in the study was more likely the explanation for the lower incidence of twinning. While it's an interesting idea to attribute the rise in the multiple birth rate to the consumption of dairy products, it is not accepted as a scientific fact. 

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Article Sources

  1. Steinman, G., "Mechanisms of twinning: VII. Effect of diet and heredity on the human twinning rate." The Journal of Reproductive Medicine, May 2006, pg. 405. PMID:16779988

  2. ​Collier RJ, Bauman DE. "Update on human health concerns of recombinant bovine somatotropin use in dairy cows." ​Journal of Animal Science., April 2014, pg. 1800-7. DOI: 10.2527/jas.2013-7383